1. Field of the Invention
The present invention relates to a method for connecting additional telephone paths and audible signals onto an existing connection between two subscriber stations which are connected together via digital, peripheral unit-associated switching matrix arrays and a digitial, central switching matrix array and central control device.
2. Description of the Prior Art
It is standard in analog telephone switching systems to connect additional telephone paths via additional windings of a repeater arranged in an existing telephone connection. Audible signals such as, for example, rapping or audible offering signals proceed to the subscribers via relay contacts connected at times to the existing telephone connection. The offering of additional telephone paths in such telephone switching systems requires involved measures with respect to level matching of the telephone paths to one another. A "designational rapping", i.e. transmission of the audible rapping signals to only one subscriber of existing telephone connection is not possible.
With the assistance of central control devices and with the assistance of digital switching matrix arrays, digital telephone switching systems allow the offering of an additional telephone path onto an existing telephone connection; but here, also, additional measures with respect to the level matching are required when connecting the telephone paths. In digital telephone switching systems, the subscribers surface feature "rapping" is usually realized in that the audible rapping signals are fit to an input of a switching matrix array and are briefly connected to an existing telephone connection in the direction of one subscriber and the telephone paths of this direction between the subscribers is briefly interrupted. After the brief connection of the audible rapping signals, the interruption of the telephone path effective in one direction is, in turn, cancelled by the central control device and by the switching matrix array. The connection of the audible rapping signals and the elimination of the interruption of the telephone paths are carried out in regular intervals until the generally administratively-defined rapping intervals have been reached. This continuous switching of the telephone path leads, first of all, to a higher load on the central control device and to an increased status message traffic between the switching system components and, secondly, leads to a destruction of the listening relationship of the subscribers of the existing connection.
The present invention relates to a method for offering additional telephone paths and audible signals onto a telephone connection existing between two subscribers in a telephone switching system of whose subscribers are connected via digital, peripheral unit-associated switching matrix arrays and via a digital, central switching matrix array, as well as by way of central control devices and controlled devices arranged in the peripheral units, whereby the peripheral units comprise the equipment for conference or, respectively, offering connections and comprise clock and tone generation.
The German published application No. 3,246,051 discloses a circuit arrangement telephone switching system wherein call progress tone signals are fed into an existing connection by way of a mixture provided for conference and offering connections. For this purpose, the mixer is equiped with a call progress tone memory and with a feed device and is connected into an existing connection by way of a first switching matrix stage or by way of first and second switching matrix stages. This assumes the connection or, respectively, the insertion of the mixture during the connection setup for every connection allowing the offering of call progress tone.